Method of making clay products



I06. COMPOSITIONS,

COATING R PLASTIC.

UNITED STATES Crc ss Heierence PATENT OFFICE METHOD OF MAKING CLAY PRODUCTS Floyd B. Hobart, Columbus, Ohio, assignor to Battelle Memorial Institute, Columbus, Ohio, a

corporation of Ohio No Drawing. Application January 14, 1937,

Serial No. 120,614 L o 5 Claims. (01. 10621) This application is a continuation in part of I or blocks which are particularly adapted for use in connection with heat or sound insulation, though it is capable of application to the making of units or aggregate to be used for structural purposes.

In the prior art, various attempts have been made to produce light-weight clay products of the type indicated. Some of these attempts have involved the mixing of clay and organic material, such as sawdust or ground cork, with water to produce a plastic mass which is molded, dried, and then fired, with the organic material being burnt out during the firing operation. One dimculty arising in this process is that heat is generated by the burning out of the combustible material and this tends to prevent uniform firing of the products.

Other efforts have involved the production of clay products of more or less cellular form, with the cell construction being formed therein by mixing the clay-like materials with reacting chemicals which produce gases within the body and cause it to be filled with a multiplicity of small bubbles. Most of these methods have required the use with the clay of appreciable amounts of setting material, such as plaster of Paris, to fix and hold the shape of the body in its porous condition until removal of the water of the mixture can be accomplished by a drying operation. These appreciable amounts of setting materials have a deleterious effect upon the hightemperature resisting properties of the resultant product.

One object of this invention is to provide a method of making a light-weight clay product which will be simple and readily controllable so that a product can be produced of any definite size and with a minimum of difliculty.

Another object of this invention is to provide a method of making a light-weight clay product which may be fired in the ordinary manner and with the usual firing temperatures, without complication from the necessity of burning out organic materials.

Another object of this invention is to provide a light-weight clay product which is of cellular form and which has high heat and sound insulating properties.

Various other objects of this invention will appear as this description progresses.

my application Serial No. 706,568, filed January 13, 1934, for Clay products and method of making the same. I

My invention preferably contemplates the making of a light-weight ceramic product by the suspension of finely divided particles of clay or like materials in a liquid, the foaming of such liquid suspension and the introduction, after foaming, of suitable materials for the conversion of the foamed mass to a condition in which it will be self-sustaining before drying has progressed to any material extent. My invention further contemplates that this conversion of the foamed mass to a self-sustaining condition shall be delayed for a period of time sufficient to permit the material to be cast into molds or otherwise formed in the desired shape.

More specifically, my invention preferably contemplates the creation of conditions wherein the clay in suspension will react with an introduced soluble silicate to effect gelation and conversion of the suspension to a solid phase so that it will retain its shape upon removal of the molds without slumpingor distortion. I have found that the cla in a water suspension will react with a soluble siIicata o p p r ratio to form amprovided the pH of the mixture of clay and water is properly selected or adjusted. I have also found that, if this mixture of clay and water has a suitable H, the elation henomenon will be sfificienl delayed to permit thorougfi mixing in of the soluble silicate with consequent improvement in the product. Likewise, I have found that gelation may be delayed with a consequent improvement in the gelled structure by the use of a soluble silicate in powdered form which also increases e t e ava mg of the silicate with the clay liquid suspension and for casting or otherwise forming. Certain clay materials have the ability to react with t .1 silicate to form complex silicates or to exc ange 10s on replace the sodium ion of the silicate with another base. When sodium silicate solutions of proper concentration are caused to react with acids or certain othe chemicals under properfih'ditibns the solutions become gelled. The time required for this gelation to occur depends upon several factors, among them concentration, temperature and acidity or alkalinity of the gelling solution, 1. e., the pH of the solution. At a pH near neutrality with other conditions suitable the gelation of such a solution occurs quickly while at increasingly higher or lower pH values the time becomes longer until at Examiner a sufiiciently high or low pH value it becomes infinite. Thus, it is possible to effect gelatign 911a r qaiuh chiaeith na 1 .e

1; possible, though not Parts Water solution of 1% sodium hydroxide 27 Sodium oleate soap i .1 5 Southern Ohio fire clay 30 Finely ground grog 30 Sodium silicate potatfiz'fia'et'tt'aa solid containing 19.4% Nazo, 62.5% $102 and 18.1% water of hydration) 1 The ingredients were added in the order given with foaming prior to the a dition of the silicate. In this mixture, the sodium hydroxide in the added, it became gelled by means of reactions with constituents of the clay.

In many cases, other chemicals may be used to advantage, instead of sodium hydroxide, to control the pH of the clay suspension. It has been found that sodium hydroxide is too strongly alkaline for control in the high pH range with some clays. With such clays, weaker alkalies such as sodium carbonate and ammonia have been used with success. Mixtures of sodium hydroxide and sodium carbonate have been used to advantage with certain specific clays. also obtained improved results with mixtures of sodium hydroxide and traces of sodium silicate with certain clays.

There are other chemicals that might be used to advantage for the purpose of bringing the clay Among these would be used. From this, it will be see'ii that e proper cHGiFe of chemicals used in my process for initially adjusting the pH of the clay susas to give dispersion of the clay materials to facilitate foaming, case A dispersed ceramic suspension in water solution has high fluidity and mobility. I prefer the minimum shrinkage results.

Clays which have been found suitable for use County, Ohio, a semiflint clay from Olive Hill, Kentucky, a plastic fire clay from Walker County, Pennsylvania, a plastic kaolin from Florida, a plastic clay from Georgia, a fire clay from When the sodium silicate was 25 106. COMPOSITIONS,

N Cross Reference COATING OR PLASTIC. 7

northern Illinois and a fire clay from Vandalia, Missouri.

In the application of my process, I preferably first determine the chemical requirements neces- Though sodium silicate has, so far, been found preferable for bringing about gelation, it will be understood that other materials may accomplish the same purpose. Thus, other alkali sili- 5 sary to give to the suspension of the clay, mixcates, such as potassium silicate, may be utilized 5 ture of clays or of clays and grogs which is to for this purpose, although the present day cost be used the alkalinity or acidity which is necesis high. sary, so that, upon the subsequent addition of Regulation of the temperature of the mixture sodium silicate, gelation will occur. I have found is desirable. Elevation of the temperature may that a definite pH must be obtained or apbe used to promote solution and to accelerate 1o proximated with each suspension, and that the gelation and consequent conversion to the solid choice of chemicals to attain this condition with phase. I have found that the heating of the each clay suspension is dictated by the nature of material while it is in the mold by passing an the clay or clay mixture which is used. In other alternating current therethrough is particularly words, certain optimum conditions are attainable effective for this purpose and may also be used 15 and the best results depend upon the use of the to facilitate drying. proper agents in relation to the ceramic ma- It will be seen that I have provided a superior terials used. method of producing light-weight, ceramic prod- The foaming Of y y p nsion in water ucts by which there can be produced cellular may be effected in other ways than by the use of units of any predetermined size and shape with 20 mechanical means. It may be effected by the ina minimum of difficulty. Moreover, these prodtroduction of air or even by the use of evolved ucts may be fired in the ordinary manner with Eases Without p rting from the scope of my the usual firing temperatures and without cominvention. The size of the cells may be such that plication from the necessity of burning out orthey will be practically invisible to the naked eye, ganic materials. 25

though they may be made larger. This will de- However, it is within the scope of my inven- D to some extentpo the o ce O foa g tion to use clay which contains inherent organic agents. matter or to add limited amounts of organic Thus, my process becomes extremely simple. matter to the mixture which will subsequently be It obviates the necessity of adding an acid or burned out during the firing of the product and 30 other chemicals to suspensions of clay in soluble thus aid in lightening the weight of the product. silicate solutions to efiect gelation. Moreover, Thus, my process may be combined with the soit makes possible a more positive control within called burn-out process of making light-weight the gelation stage. I preferably use sodium siliceramic products when advantages are obtained 'cate with a soda 0 silica ratio of about 1:3 to 1:4, thereby. wherein the silicates are readily renfi'ere' H H!"- Furthermore, my method is such that the stable and gelation occurs as a result of reaction density of any product resulting therefrom may with the ceramic materials in the mixture. be effectively controlled to produce a cellular I P f rably use a odium silicate hich is in unit which is extremely light in weight but, also,

40 powde ed florm a d WHICH 1S Slowly soluble m unusually strong. Likewise, my method may be m we er, as as een specified in the example given modified, with unusual ease, to produce units above. A liquid sodium silicate may be used but, which excel either in heat insulating properties with some clays, it is not as desirable, since it or in sound insulating properties as desired. causes a flocculating or thickening of the It will be seen that I have provided a method suspension before gelation and introduces mixing wherein the conversion of the foamed mixture and molding difficulties. The slow solubility of to the solid phase may be protracted sufliciently the powdered sodium silicate overcomes these to give ample time for casting, molding or exdifiiculties, since it allows ample time for mixing trusion to form units of the desired shape and, the silicate into the suspension and for molding at the same time, to attain self-sustaining qualiwhile the suspension is still in a fluid condition. ties with such promptness that the product can However, the powdered sodium silicates are be set out for drying without delay. more expensive than those in liquid form and It will also be evident that my delayed gelation the latter should be considered when the clays permits of adequate agitation of the foamed mixand the required quality of the product render ture before gelation takes place. The delayed their use permissible. For example, I have found gelation also permits careful performance of the 35 with Bedford shale from Franklin County, Ohio, casting or forming operation before gelation and a surface clay from Delaware County, Ohio, begins. that the addition of sufficient silicate in liquid After gelation has been effected, the formed form to cause gelation of the mixture according units may be dried in the usual way. Following to my process may be made without greatly afdrying, the units may be fired by the usual cem footing the colloidal nature of the dispersion. ramic practice, the time and temperature factors It appears that in the foaming of my clay depending upon the properties of the clay or suspension, the proper dispersion of the clay other ceramic materials which have been used. particles assists in forming a continuous film of My invention is not necessarily limited to the these clay particles around the bubbles. The Production of fQrmed units- It may be utilized o5 gelation of the mixture in dispersed condition produces a cellular structure wherein the cells are substantially spherical in form with smooth dense walls. By regulating the ratio of ceramic materials to the solution used in the dispersed mixture, I may make the cells non-communicating or communicating, as desired, the former being particularly desirable for heat insulation material and the latter for sound insulation ma- 76 terial.

for the purpose of producing light-weight ceramic material which may be broken up to form light-weight aggregate. Such light-weight aggregate may be used loosely or it may be combined with some binding or cementing material for the production of bricks, blocks or slabs which have suificient strength for building purposes or the like while, at the same time, being unusually light.

By the term ceramic product" I mean to include products made from clay or clay-like, earthy or other mineral materials or the mixtures thereof which may be more or less plastic in a moist condition and which becomes sintered, fused or vitreous when burned at a sufficiently high temperature as for example: fire clay, kaolin, alumina minerals, silica minerals, et cetera.

By the term "grog as used in this description, I mean to include such materials as calcined clays, ground firebrick or other clay ware and, in addiiton, the natural occurring non-plastic mineral materials such as are commonly used in the ceramic arts.

While the terms "gelation" and flocculation are sometimes used loosely in the art to describe the same thing, I herein use these terms to indicate different phenomena. Thus, it will be seen from the above description that my method contemplates the use of the phenomenon of gelation either of a dispersed or a fiocculated ceramic suspension. The gelation phenomenon to which I refer involves the conversion of a liquid ceramic mixture to a self-sustaining unit by means of or with the aid of a soluble silicate within the mixture which is caused to become unstable and convert the mixture into a solid phase. The term flocculation has been used in this description to denote a change in condition which results in the changing of the clay particles in the mixture from a discontinuous to a continuous phase by the introduction of a flocculating agent which results in the collecting together of such clay particles and the consequent stifiening of the mixture.

Numerous advantages of my invention, other than those set forth specifically, will appear from the preceding description and the appended claims.

Having thus described my invention, what I claim is:

1. The method of making a ceramic product which comprises making a suspension of ceramic material in water wherein the ceramic material has been selected because of its ability to effect gelation of a soluble silicate to be subsequently introduced and wherein the suspension has a pH value suitable for attainment of gelation at a desired time, and adding the soluble silicate in powdered form to bring about gelation and consequent conversion of the suspension from a liquid to a solid phase.

2. The method of making a light-weight ceramic product which comprises making a sus- P nsion of ceramic material in water wherein the ceramic material has been selected because of its ability to effect gelation of a soluble silicate to be subsequently introduced and wherein the suspension has a pH value suitable for attainment of gelation at a desired time, foaming such suspension, and adding the soluble silicate in powdered form to bring about gelation and consequent conversion of the suspension from a liquid to a solid phase.

3. The method of making a light-weight ceramic product which comprises making a suspension of ceramic material in water wherein the ceramic material has been selected because of its ability to effect gelation of a soluble silicate to be subsequently introduced and wherein the suspension has an alkaline pH value suitable for attainment of gelation at a desired time, foaming such suspension, and adding the soluble silicate in powdered form to bring about gelation and consequent conversion of the suspension from a liquid to a solid phase.

4. The method of making a light-weight ceramic product which comprises making a suspension of ceramic material in water wherein the ceramic material has been selected because of its ability to effect gelation of a soluble silicate to be subsequently introduced, adding a chemical to adjust the pH of the suspension to an alkaline Value suitable for attainment of gelation at a desired time, and adding the soluble silicate in powdered form to bring about gelation and consequent conversion of the suspension from a liquid to a solid phase.

5. The method of producing a light-weight ce-' ramic product which comprises producing a foamed ceramic-liquid suspension and mixing therewith a slowly soluble sodium silicate powder that will slowly bring about gelation.

FLOYD B. HOBART. 

